This History Channel series, which moved to H2 for season four, revolves around the idea that earlier civilizations developed their most advanced ideas by means of extraterrestrial influence. A range of speakers, from respected scholars to more conspiracy-minded thinkers (“ancient alien theorists”), sift through the evidence, while a dramatic score juices each revelation. The most famous participant, Erich von Däniken, whose 1968 bestseller Chariots of the Gods encouraged this mode of thinking, figures prominently. Viewers who’ve watched previous seasons will be familiar with the basic format, as well as the primary theories about alien-inspired architecture and the like, since there’s significant repetition from year to year